ACARS (Aircraft Communication Addressing and Reporting System) is a digital data link system transmitted via radio that allows airline flight operations departments to communicate with the various aircraft in their fleet.
ACARS is a VHF digital transmission system used by many military and civilian aircraft. It is analogous to “email for airplanes,” as the registration of each aircraft is it's unique address in the system developed by ARINC (Aeronautical Radio, Inc.). Traffic is routed through services such as the ARINC and SITA computers to the proper company or airplane, relieving some of the necessity for routine voice communication with the company. With ACARS, such routine items as departure reports, arrival reports, passenger loads, fuel data, engine performance data, and much more, can be requested by the company and retrieved from the aircraft at automatic intervals. Before the advent of ACARS, flight crews had to use voice transmission to relay this data to their operations on the ground.
The ACARS system comprises the following elements:
1. The Airborne Subsystem, onboard the aircraft, which consists of the:                a.) Management Unit Receives ground-to-air messages via the VHF radio transceiver, and controls the replies.        b.) Control Unit is the aircrew interface with the ACARS system, consisting of a display screen and printer.        
2. The ARINC Ground System, which consists of all the ARINC ACARS remote transmitting/receiving stations, and the ARINC computer and switching systems.
3. The Air Carrier C2 (Command and Control) and Management Subsystem, which is basically all the ground based airline operations such as operations control, maintenance, crew scheduling and the like, linked up with the ACARS system.
Messages fall into two types characterized by their direction relative to the aircraft: “Downlinks” are those ACARS transmissions that originate in the aircraft, and “uplinks” are those messages sent from the ground station to the aircraft.
Airlines pay for transmission of data over the ACARS system according to numbers of bits sent and received. Character based protocols limit the set of characters that can be transmitted. Some characters in the 8-bit lexicon are reserved by character-based protocols to be used as delimiters. When so assigned, the reserved characters cannot be present in the character stream. The admissible number of characters that may be present in the data steam is, then, fewer than the 128 characters expressible in an 8-bit stream.
What is missing in the art are methods and systems for a reduction of the transmission bits for a more economical, loss-less encoding and transmission of data.